As a
travel agent, I participated in a conference call from the TSA regarding the new requirements several months ago.
This will be phased in over the next year or two, as airlines update their systems to not only collect this information, but to transmit it to TSA 72 hours (or at time of ticket purchase if within 72 hours) before the flights. TSA will supress the boarding pass if the name-gender-DOB is on their watch list for further security checks at the airport. The TSA transmission part will not happen all at once, but as each airline's system complies. Once TSA clears the names (supposedly will take just seconds) the boarding pass can be printed, either online or at the airport. Knowing the airlines, it might be a while before all are fully compliant, so the TSA is phasing this in.
IF you are a match on the watch list the airline cannot print your boarding pass. To prevent this, those who know ahead of time that they are a match can apply to TSA for a "redress number", which will be a permanent number assigned to that person to be given with every airline reservation. This basically says that TSA has investigated you already and you are not a threat. The airlines and travel agents will collect this redress number with your DOB info, so obviously the airlines will create a field for it. If you don't have the redress number in your reservation, no boarding pass until you get the once over from TSA security.
Secure Flight is basically taking the security function from airline discretion and making it electronic through the TSA. Once fully implemented the program is supposed to speed up security and prevent so many people from being pulled over when their names are a close match to the watch list. For the time being, slight name variations, like a middle name or initial, is allowed. But once in place there must be an exact name and DOB and gender match for all airline travel, not just international as is currently the case.